I am working on a Lesabre that has no heat. I suspect the system is air locked, but need to make sure that the vehicle does not have a heater valve. Here are the symptoms:

All vents work correctly.

Mode door is working-- you can hear the airflow change as the temp selector is moved from cold to hot.

With car warmed up, Radiatior hoses are hot, but heater core hoses are cold. The temp change appears to be happening inside the intake manifold on the upper heater core hose.

Coolant needs changing-- looks like water with rust particles.

This is a manual system.

Suggestions?

As I recall there is an inline valve that opens and closed based on the demand for coolant to flow through the heater core. Or your system could have a deadhead in the line somewhere causing the coolant to bypass the heater core. I'd start by disconnecting the heater core lines and see if a garden hose reveals a blockage or not.

As I recall there is an inline valve that opens and closed based on the demand for coolant to flow through the heater core. Or your system could have a deadhead in the line somewhere causing the coolant to bypass the heater core. I'd start by disconnecting the heater core lines and see if a garden hose reveals a blockage or not.

I second this.

Dan